The World Health Organisation on Tuesday warned that swine flu was causing unusually serious levels of infection among indigenous people in Canada, as it geared up to formally announce a global pandemic.

Keiji Fukuda, the agency’s assistant director-general, said a “larger number than expected” of young indigenous people was being hospitalised, in a trend that raised the prospect that the virus may have a more severe impact on some groups of people, similar to the experience in Mexico.